As such a conveyance system, for example, the configuration disclosed in Japanese Patent Laid-Open No. 10-111719 is conventionally provided. This conventional configuration is provided with conveying trucks supported and guided along a main track and a branching track. Each of the tracks comprises a bottom wall, a right and a left side walls, and a top wall, and is shaped like a duct by forming a slit in a width-wise center of the top wall, a slit extending along a longitudinal direction. At least at a branching point, a guide along the main track and a guide along the branching track are provided. Further, the conveying trucks are each provided with a guide member following the guides and a directing mechanism for directing the guide member to one of the guides.
The guides comprise guide rails made of a magnetic body and extending along the main track and the branching track, respectively. The guide member comprises a magnetic roller which is directed to either one of the guide rails via an arm or the like.
With the above conventional form, however, the main and branching tracks must be provided with separate guide rails made of a magnetic body. This is cumbersome in assembling or constructing this form. Further, since the main and branching tracks are shaped like ducts, dust or the like collects on the bottom walls of the tracks, which cannot be cleaned easily. Accordingly, it is not easy to employ this conventional form cannot for clean rooms, where clean air is blown downward.
Furthermore, layouts that enable branching and juncture are limited. For example, it is difficult to provide a layout in which the tracks extend in parallel and in which the conveying trucks are shifted between the tracks. As a construction in which the conveying trucks are shifted between the tracks, a swinging table form disclosed in Japanese Patent Laid-Open No. 11-222122 is provided. This invention, however, requires a complicated structure and also requires the conveying truck to stop running between the tracks.
Further, since the main and branching tracks are shaped like ducts, for example, formation of a loop line requires separate exclusive parts to be prepared for a linear portion and a curve portion. In particular, the track of the curve portion is expensive.